Devices of the above type typically comprise a case made of thermoplastic material, within which are contained a thermal actuator and, at least partially, an actuating shaft. The actuator in turn comprises a body made of electrically and thermally conductive material (e.g. steel), containing a temperature-expandable material, such as a wax, into which is at least partially immersed a piston, destined to drive the actuating shaft; said body is in contact with an electrical heater, usually a PTC resistor.
Actuator devices of the above type are described, for example, in the documents U.S. Pat. No. 5,572,869, U.S. Pat. No. 6,240,728, U.S. Pat. No. 6,121,588, U.S. Pat. No. 5,968,395, U.S. Pat. No. 5,656,986.
In order to electrically power the heater of the device, it is provided with two contact blades or terminals, each having a portion inside the case and a portion projecting from the case. The inner portion of said blades defines respective elastic terminations or wings, to achieve contact with the body of the actuator and the heater; the projecting portions of the blades instead are shaped in the manner of male “faston” terminals or contacts. On each of said projecting portions is fitted a respective female “faston” connector, which constitutes the terminal element of a respective power supply cable; said connection operation is usually performed manually by an operator, who physically couples each female faston connector on each respective male faston terminal of the actuator device.
The Applicant has noted, as a result of practical simulations conducted, that the aforesaid prior art of electrically connecting actuator devices is a source of possible drawbacks.
First drawbacks occur when known actuator devices are used in particularly challenging work conditions, such as those characterised by high vibrations. For example, in case of use of an actuator devices of the type indicated above on laundry washing machines, the vibrations in particular operating conditions (high speed centrifuges with unbalanced load) and the thermal stresses whereto are subjected the contact blades and the thermoplastic case of the device can, in the long run, compromise the quality and soundness of the electrical connection.
Other drawbacks are linked to the configuration of said male faston terminals, which are exposed outside the body of the actuator device, favouring the risk of accidental contact with other parts; in practice, it has been observed that sometimes the female faston is not completely coupled on the male faston of the device, also due to the high insertion force required, and this determines the presence of an area outside the actuator device that is not protected or not electrically isolated, and is a possible cause of accidental contacts and/or electrocution risks.
The use of single faston connectors, typical of the prior art, can also determine the risk of erroneous wiring, where for example to the electro-thermal device are connected the female faston connectors destined to another device, e.g. a thermostatic switch, and vice versa; in this situation, therefore, short circuits may occur, which are able severely to damage the electrical system of the electrical appliance and/or of the control apparatus. In other cases, instead, there is a need to connect multiple thermoelectric actuators of the same type, but coupled with different apparatuses (e.g.: diverting valves, detergent dispensers, etcetera), though still in the same apparatus; considering that, in the prior art, the type of connector is the same for every actuator of the various devices, there is a risk to connect a device instead of another one. Moreover, in the production phase, different types of thermoelectric actuators are often produced; the actuators may be externally unchanged but may be differentiated by their internal components (e.g. the type of heater), and/or by the testing parameters, which may differ from one model to another; to date, this diversity is made apparent only by means of different codes (captions) or colours, which in any case cannot prevent an erroneous mounting and/or connection of a thermoelectric actuator of a first type instead of a thermoelectric actuator of a second type, with the obvious consequence that the operation will not be correct.
In its general terms, the object of the present invention is to solve one or more of the aforesaid drawbacks, and in particular to obtain an electro-thermal actuator comprising electrical interconnection means able to guarantee a connection that is certain, reliable and secure over time.
This and other objects, which shall become readily apparent below, are achieved according to the present invention by an electro-thermal actuator device having the characteristics set out in the appended claims, which are an integral part of the present description.